1. Field of the Invention
The present invention relates to a CMOS variable gain amplifier (VGA), which can provide a function of controlling a gain of input signals with both low distortion and high-speed operating range, by allowing the amplifier to have a variable gain by controlling the value of an output current of its drain terminal against a gate voltage of the NMOS transistor, can control a voltage gain with a wide gain control range and can be embedded in the IC.
2. Background of the Related Art
Performance parameters of VGA that must be considered in designing the CMOS variable gain amplifier may include maximum of signal-to-noise ratio (SNR) for a desired signal value, a frequency bandwidth, low distortion, the input signal level that guarantees desired linearity, noise characterisitcs, gain control range, and the like. Further, its dependence on the temperature variation or supply voltage can not be excluded. In particular, it is not easy to design a CMOS VGA circuit having the operating frequency range of over 100 MHz in view of device technology characteristics. Furthermore, due to limitations in reduction of the threshold voltage in the MOS device, the input/output signal level is limited. It is, thus, difficult to expect a smooth operation of VGA for a low power supply because of smaller input signal range.
Therefore, it is difficult to implement the CMOS variable gain amplifier with a low power consumption characteristics at the low voltage as an integrated circuit.